1. Technical Field
The present invention relates to detecting a leak. More particularly, the invention concerns an apparatus for detecting a leak of a liquid, by detecting a lowering of the top surface of the liquid.
2. Description of Related Art
Drain pipes, which may be called waste lines, are commonly installed during the construction of buildings and paved areas. Waste lines may be used in various types of drain systems, which may include, for example, sewer, lab, kitchen, or other types of drain systems. Pipes used for waste lines may be made of various materials, including cast iron or plastic, and in some instances double containment pipes that include an inner pipe and an outer pipe may be used.
Waste lines often include horizontal pipes that are placed in trenches in the ground, and vertical pipes (which may be called vertical risers or vent pipes) that are connected to the horizontal pipes. A concrete slab may be formed over the pipes in the trenches, and the vertical pipes may be connected to various locations in a building. After waste lines are installed, for example by placing pipes in trenches and attaching vent pipes, a building inspector usually tests the waste lines to make sure they hold water.
In preparation for the building inspector's test, the ends of the waste lines are capped to make them water tight, and a ten foot vertical pipe is attached to the waste lines. The ten foot vertical pipe is used to create head pressure in the waste lines when the ten foot vertical pipe and the waste lines are filled with water. To conduct the test, the ten foot vertical pipe and the waste lines are filled with water, and if the water level in the ten foot vertical pipe does not drop after fifteen minutes, the waste lines are “signed off” by the building inspector.
After the waste lines are approved by the building inspector, typically the pipes in the trenches are covered with dirt and the trenches are filled with dirt, in a process called back filling. Frequently, sand and rock are placed on the dirt to form a final sub grade, and then concrete is poured on the sand and rock to form a concrete slab.
Pipes in the waste lines are often damaged during construction after the waste lines are approved by the building inspector. Various construction activities can result in damage to waste lines. For example, waste lines can be damaged by back filling machines or shovels used during back filling, or when electrical lines are placed underground, or when screed pins are installed to indicate the top surface of the slab, or if workers lean on vent pipes, or by vandals. In many instances, leaks in the waste lines are not discovered until after the slab has been poured, because workers may be unaware that the waste lines have been damaged, or because subcontractors may be uneager to disclose that they have damaged the waste lines.
The existence of damage to waste lines is difficult to observe because the damage to the waste lines, and the water that may leak from the damaged waste lines, are usually hidden beneath back fill and the final sub grade. Also, because leaks are often not discovered until after the slab has been poured, it is difficult to determine who is responsible for the damage. Locating and repairing leaks in waste lines after the slab has been poured is frequently very costly and can result in significant delays in construction. For example, finding a leak may require saw cutting, and breaking and removing many portions of the slab until one or more leaks are found. Consequently, it is desirable to detect and repair leaks in waste lines before the slab is poured. However, existing techniques do not adequately detect leaks in waste lines during the construction process before a slab is poured.